钙钛矿过渡金属氧化物极性/非极性异质界面二维电子液体行为及其应用探索

The multiple degrees of freedoms, e.g., charge, spin, orbital, and lattice in transition metal oxides usually couple strongly with each other. Therefore, in sharp contrast to the two-dimensional electron gases at the interfaces between conventional semiconductors, novel quantum effects caused by strong couplings between the multiple degrees of freedoms, in addition to conductivity, may emerge at the conducting interfaces between transition metal oxides, which is called two-dimensional electron liquids (2DELs). However previous studies on the 2DELs are mainly focused on the LaAlO3/SrTiO3 system. Here based on previous experiences on the transition metal oxide heterostructures, our team will develop the laser molecular beam epitaxy technique to grow a series of perovskite transition metal oxide polar/nonpolar heterostructures, explore the strong-coupling induced 2DEL behaviors including magnetism and superconductivity and their applications in photovoltaics and spintronics. The team members will take full advantage of the rich experiences in the characterizations using high-resolution transmission electron microscopy and synchrotron diffraction to establish the stoichiometry-structure-property relationships. Our study will reveal the coupling principles between the multiple quantum degrees of freedom, discover the novel interfacial 2D quantum effects, extend our understanding of the new picture of 2DEL at the interfaces between perovskite transition metal oxides, and lay the foundations of materials and principles for the next-generation quantum devices based on oxide heterostructures.

过渡金属氧化物中电荷、自旋、轨道和晶格自由度通常有很强的耦合，因此其界面不仅可能导电，还可能出现多自由度强耦合导致的新奇量子效应，即二维电子液体行为。这与常规半导体界面的二维电子气行为形成鲜明对比。然而过去对过渡金属氧化物界面二维电子液体的研究主要集中在LaAlO3/SrTiO3体系。本项目团队将在氧化物异质结研究基础上，发展激光分子束外延技术制备一系列钙钛矿过渡金属氧化物极性/非极性界面体系，探索由于强耦合导致的界面磁性、超导等二维电子液体行为以及这些界面体系在光伏、自旋器件方面的应用。项目成员将充分利用高分辨率透射电镜和同步辐射衍射方面的丰富经验，建立氧化物界面的组分-结构-特性关系。我们的研究将揭示氧化物界面量子自由度的耦合规律，发现由此导致的新奇二维量子效应，拓展对过渡金属氧化物界面二维电子液体这一新物理图像的认识，为发展基于氧化物异质结的新一代量子器件打下坚实的材料和原理基础。

探索和调控钙钛矿过渡金属氧化物极性/非极性异质界面二维电子液体行为，对理解氧化物界面丰富物性产生机制，设计基于氧化物的新型电子学器件具有重要意义。我们在相关领域取得了若干进展：（1）实现了极性/非极性氧化物异质结二维电子液体自旋轨道耦合强度随能带填充非单调变化的电学和光学调控。（2）在基于LaAlO3/SrTiO3异质结的隧穿器件中发现了多种多体效应共存以及轨道依赖的近藤效应。（3）通过极性/非极性氧化物异质结的内建极化电场极大增强了近邻石墨烯的紫外光电导效应。（4）首次通过界面效应在钙钛矿锰氧化物体系诱导实现电子相的摩尔图案调控。（5）发现准一维锰氧化物单晶纳米线的量子逾渗和新相图；通过激光辐照调控了锰氧化物薄膜的电子相。（6）基于同步辐射表征技术阐明多个钙钛矿氧化物体系物性与结构的关联机理。在该项目执行期间，共发表SCI论文66篇，包括5篇Phys. Rev. Lett.，2篇Nat. Commun.，1篇Adv. Mater.，3篇Nano Lett.，1篇Angew. Chem. Int. Ed.和2篇ACS Nano。培养17名博士生毕业，16名硕士生毕业，1名博士后出站。